(a) Field of the Invention
The invention relates to a magnetic drive sealless plump having an auxiliary circulating channel for cooling between the bearing and the capsule thereof, such that cooling effect by convection exists at both the interior and exterior of the bearing thereof, thereby ensuring that excessive heat is not produced.
(b) Background of the Invention
FIG. 1 shows a prior magnetic drive centrifugal pump, which includes a casing 100 combined with a shell 200. At the front part of the casing 100 is a suction opening 101 and at the top thereof is a discharge opening 102. At the center of the shell 200 is a shaft 201 enveloped with a bearing 202 further enveloped with a capsule 203. In the capsule 203 is a driven magnet 204 and the capsule 203 is extended forward into the casing 100. At the front of the capsule 203 is positioned an impeller 205. During the rotation of the impeller 205, the fluid thereof is lifted from the suction opening 101 to the discharge opening 102 through the impeller 205. The driven magnet 204 is driven by the drive magnet 206 which is attached to a motor. And between these two magnets is a shell 200 to prevent entry of liquid from the outside. In a normal operation of the pump, the pressure difference between the input and output of the impeller 205 is employed to have a small amount of fluid thereof flow to the rear part of the impeller 205 through the passage between the outer side of the capsule 203 and the inner side of the shell 200, and heat produced is taken away through a groove between the bearing 202 and the shaft 201. Among the circulation route thereof (gaps A, B, C, D, and E), only gaps D and E have a convection effect for cooling. Thrust rings 207 are positioned adjacent the impeller 205 and the capsule 203.
However, in an abnormal operation of the pump caused by malfunctions of control instruments, mishandling during operation, congestion caused by waste fluid, or insufficient suction liquid level for instance, may cause the pump to perform dry running. Since the medium of convection for cooling is air, which can only carry away a limited amount of heat, and therefore the temperature of the bearing 202 and the shaft 201 is rapidly elevated, thus resulting in serious damage of the pump. Once dry running takes place, the bearing 202 and the shaft 201 are abraded, and the capsule 203 is also deformed from the heat produced. More particularly, the capsule 203 is generally made of plastic that deforms easily from heat, further increasing the abrasion due to the dry running, and therefore the pump becomes unfit for its application.
In order to prevent deformation of the capsule 203 from heat, provision of additional heat resistant materials to the inner periphery of the capsule 203 has been attempted. However, the addition of the heat resistant materials thereof not only complicates the manufacturing process and increases the production cost, but also has unsatisfactory effects due to long-term dry running of the pump that causes the temperature of the bearing 202 and the shaft 201 to rise up to 220° C. Therefore, if heat produced is held within the pump in a contained manner, the result is unsatisfactory.